{-# LANGUAGE TemplateHaskell #-}

-- | Command prefix parsing effect
module CalamityCommands.ParsePrefix
    ( ParsePrefix(..)
    , parsePrefix
    , useConstantPrefix ) where

import qualified Data.Text.Lazy                       as L

import qualified Polysemy                             as P

-- | An effect for parsing the prefix of a command.
data ParsePrefix msg m a where
  -- | Parse a prefix in a message, returning a tuple of @(prefix, remaining message)@
  ParsePrefix :: msg -> ParsePrefix msg m (Maybe (L.Text, L.Text))

P.makeSem ''ParsePrefix

-- | A default interpretation for 'ParsePrefix' that uses a single constant prefix.
useConstantPrefix :: L.Text -> P.Sem (ParsePrefix L.Text ': r) a -> P.Sem r a
useConstantPrefix :: Text -> Sem (ParsePrefix Text : r) a -> Sem r a
useConstantPrefix Text
pre = (forall (rInitial :: EffectRow) x.
 ParsePrefix Text (Sem rInitial) x -> Sem r x)
-> Sem (ParsePrefix Text : r) a -> Sem r a
forall (e :: (* -> *) -> * -> *) (r :: EffectRow) a.
FirstOrder e "interpret" =>
(forall (rInitial :: EffectRow) x. e (Sem rInitial) x -> Sem r x)
-> Sem (e : r) a -> Sem r a
P.interpret (\case
                                        ParsePrefix msg -> Maybe (Text, Text) -> Sem r (Maybe (Text, Text))
forall (f :: * -> *) a. Applicative f => a -> f a
pure ((Text
pre, ) (Text -> (Text, Text)) -> Maybe Text -> Maybe (Text, Text)
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> Text -> Text -> Maybe Text
L.stripPrefix Text
pre Text
msg))